1. Field of the Invention
The present invention relates to a combined cycle power plant that combines a gas turbine plant and a steam turbine plant.
2. Description of Related Art
A combined cycle power plant is a power system that combines a gas turbine plant and a steam turbine plant, and heat energy in the high temperature region is allotted to the gas turbine and heat energy in the low temperature region is allotted to the steam turbine. Heat energy is efficiently recovered and used, and recently, in particular, this power system has received much attention.
In this combined cycle power plant, research and development is advancing concerning the one point related to increasing efficiency, that is, how high the high temperature region of the gas turbine can be raised.
In contrast, in the formation of the high temperature region, it is necessary to provide a cooling system to maintain the heat resistance of the turbine structure body, and conventionally air has been used as the cooling medium in this cooling system.
However, to the extent that air is used as the cooling medium, for example, even when the high temperature region can be attained, when considering both the power loss necessary for increasing the air used in cooling to the necessary pressure by the air compressor and the result that the energy of the gas decreases because of the decreasing of the average gas temperature due to the final mixing of air used in the cooling of parts inside the turbine flow path transited by the high temperature gas, an increase over the present heat efficiencies cannot be expected at this point in time.
In order to solve this problem and implement an increase in efficiency, switching the above cooling medium in the gas turbine from gas to steam has been proposed.
One example of this is Japanese Unexamined Patent Application, First Publication, No. 05-163960. However, although the invention disclosed in this publication discloses the notion of using steam as a cooling medium in a gas turbine, there remain many problems in the details that must be thought about and solved.
For example, the steam heated to a high temperature by cooling the high temperature cooled part of the gas turbine is introduced into a intermediate pressure turbine by being mixed with steam supplied from a reheater, but currently the technology disclosed concerning this area is limited to the supply system for the working steam, and here no concrete consideration or examination is made of the location of the positions or how they are combined.
That is, attempting to cool the high temperature cooled part of the gas turbine is presently still at the trial and error stage, and actually there are many problems to be elucidated and resolved.
As described above, starting with the disclosures of Japanese Unexamined Patent Application, First Publication, No. 05-163960, as conventional technology, there is no particularly deep examination of the mixing of a plurality of steams introduced into the intermediate pressure turbine, and the inventors seem to be unaware of the problems.
However, because the respective characteristics, for example, the pressure and temperature, of the steam heated to a high temperature by cooling the high temperature cooling part of the gas turbine as described above and the steam supplied from the reheater are different, when these gases are introduced into the intermediate pressure turbine in a state of incomplete mixing, steam having high temperature or steam having a low temperature with respect to the set temperature are introduced into the turbine as they are, and there is the concern that this might cause damage to the turbine body.
In addition, when using a structure in which the plurality of mixed steams is held in the vicinity of the intermediate pressure turbine in the tubing, the amount of tubing is large and this size leads directly to an increase in cost. Furthermore, there are concerns about temperature differences in the tubing and the tubing cracking due to the thermal stress.